After you put the steel wool in the gap use lots of resin to tin existing metal. You may need to remove the bead on it to prevent problems. You may be able to get by with a good iron rather than torch on that metal.

God so loved the world He gave his only Son...
...Believe in Him and have everlasting life.
John 3:16

When doing cowboy action we used to fill in the gap with Brownells Acra glass gel dyed black mixed with atomized steel. I have a 12ga double that is done this way that has withstood thousands of rounds. Make sure you rough up the steel first. I used a needle file to get down in there about 2" deep.

Actually still wondering, but it needs something. I like the epoxy idea. I can rough up the inside, fabricate the piece longer than it is wide, have it engraved, stuff in steel wool, and then epoxy it in. I am starting to like this site! Good ideas!